Certain applications require relief or check valves that are responsive to critical low pressures within close tolerances. For example, a blood pressure cuff requires a reliable relief valve that predictably and consistently responds to a predetermined relief pressure setting to limit the maximum pressure that can be applied through the cuff.
There are several drawbacks to the prior art relief valve designs currently used: Firstly, the seal on the poppet of a typical prior art relief valve has such a large surface area that it tends to stick to the valve body, resulting in relief pressures that sometimes exceed by up to 25 percent the desired pressure relief setting. Secondly, the seal is usually retained within a groove in a separate metal poppet, which can lead to malfunctions such as leakage of pressurized air past the closed poppet through its seal groove. The seal is squeezed into the groove and conforms thereto at sufficiently high pressure. A tight seal assures close tolerance "cracking-pressure and also close tolerance resealing. Pressure below the threshold to deform the seal to fit the groove cannot provide a close tolerance seal. Thirdly, the poppet of the typical prior art relief valve is subject to excessive vibration when unseated, sometimes causing the poppet to reseat off-center, leading to leakage and to inconsistent, unpredictable and inaccurate relief pressures.
From the foregoing it will be apparent that there is a need for a low pressure sensitive valve that responds accurately and consistently to a predetermined pressure setting, within close tolerances. To this end, objectives of the invention are to provide such a valve with (1) a poppet seal that does not stick or leak, and (2) a poppet that is relatively vibration-free when unseated and consistently reseats in a fully closed position.